This weekend I met up with some friends to have a few drinks. This was a fairly upscale restaurant, that has a large bar area. After many hours of heavy drinking, I stumbled over to the bathroom to relieve myself.
I initially went to the bathroom to pee, but while peeing, I came to the realization that I had to poop. In my drunken stupor, I thought it would be hilarious to take an upperdecker. (For those of you unfamiliar with an upperdecker, it's when you poop in the top part of the toilet. When the next person flushes the toilet, all of the poo water flushes down and makes a smelly mess.)
There was another gentleman waiting for the stall as I came out. Laughing hysterically, I stumbled out of the stall and schlepped my way back to the bar. Little did I know, the gentleman who used the stall next was an employee of the restaurant.
Long story short... I'm not welcomed there anymore. Can I sue?
I doubt it but there probably is a sign that says "We reserve the right to refuse service to anyone." As far as litigation, the restaurant probably has small but demonstrable damages if the story is true as relayed.
It wouldn't matter what you did in their bathroom (although I'm doubting it happened at all), nor the posting of any sign on their premises.
It is the legal right of any proprietor to refuse service to an individual, so long as that service is not considered an "essential service" and as long as the motivation for that refusal is not based against human rights, such as refusing service to members of a certain race, creed, religion, gender, disability, etc.
Regardless, you can sue them if you want. Just don't expect to win.